From 513c0a0f4602018a49d8fd2dfa24670a3fa08ac9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Wed, 26 Feb 2020 21:44:48 +0100
Subject: [PATCH] daemon: Drop 'AT_STATX_DONT_SYNC' flag upon EINVAL.

Fixes <https://bugs.gnu.org/39727>.
Reported by Paul Garlick <pgarlick@tourbillion-technology.com>.

* nix/libstore/gc.cc (LocalStore::removeUnusedLinks) [HAVE_STATX]: Add
'statx_flags' static variables.  Clear 'AT_STATX_DONT_SYNC' flag from
'statx_flags' when 'statx' returns EINVAL.
---
 nix/libstore/gc.cc | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/nix/libstore/gc.cc b/nix/libstore/gc.cc
index 77d7fa2dc7..8bc4e01eb0 100644
--- a/nix/libstore/gc.cc
+++ b/nix/libstore/gc.cc
@@ -581,15 +581,27 @@ void LocalStore::removeUnusedLinks(const GCState & state)
 #ifdef HAVE_STATX
 # define st_size stx_size
 # define st_nlink stx_nlink
+	static int statx_flags = AT_SYMLINK_NOFOLLOW | AT_STATX_DONT_SYNC;
 	struct statx st;
-	if (statx(AT_FDCWD, path.c_str(),
-		  AT_SYMLINK_NOFOLLOW | AT_STATX_DONT_SYNC,
-		  STATX_SIZE | STATX_NLINK, &st) == -1)
+
+	if (statx(AT_FDCWD, path.c_str(), statx_flags,
+		  STATX_SIZE | STATX_NLINK, &st) == -1) {
+	    if (errno == EINVAL) {
+		/* Old 3.10 kernels (CentOS 7) don't support
+		   AT_STATX_DONT_SYNC, so try again without it.  */
+		statx_flags &= ~AT_STATX_DONT_SYNC;
+		if (statx(AT_FDCWD, path.c_str(), statx_flags,
+			  STATX_SIZE | STATX_NLINK, &st) == -1)
+		    throw SysError(format("statting `%1%'") % path);
+	    } else {
+		throw SysError(format("statting `%1%'") % path);
+	    }
+	}
 #else
         struct stat st;
         if (lstat(path.c_str(), &st) == -1)
-#endif
             throw SysError(format("statting `%1%'") % path);
+#endif
 
         if (st.st_nlink != 1) {
             actualSize += st.st_size;